ABSTRACT Cocaine (COC) is a highly addictive and a potent central nervous system stimulant, and abuse of this drug can result in significant long-term neurocognitive deficits in the human brain. Conventional pharmacotherapies for COC abuse have had limited clinical effectiveness. An alternative treatment approach that could become a powerful tool to help prevent cocaine abuse relapse, is vaccination against COC, which has shown promising results in both animal and human studies. Such vaccines can elicit high concentrations of antibodies (Abs) that bind cocaine, retain it in the circulation, and inhibit its entry into the brain. Ideally, when a vaccinated individual might use the drug, the characteristic increase in drug cravings (drug reinforcement) will be diminished or completely inhibited. The first human trial with cocaine conjugate vaccines demonstrated reduced cocaine use in subjects who had good Ab responses, but only a third of immunized subjects achieved adequate blocking levels of anti-cocaine Abs, and furthermore Ab levels declined rapidly after the vaccine booster doses ended. Susceptibility to cocaine abuse relapse is highest for several months after withdrawal from the drug, and so low initial responses in many subjects and a rapid decline of the Ab titers in good responders within weeks after completion of the booster schedule could substantially reduce the impact of this cocaine vaccine. Immune responses are ordinarily tightly regulated to permit a rise and fall of immunity with the decline mediated by regulatory T cell (Treg) suppression; so modulating Treg function using toll like receptor (TLR)-based small molecules and anti-costimulatory molecules can markedly enhance immune responses. This proposal seeks to address these critical vaccine problems by innovative immunological studies, which will include novel cocaine conjugate construction, nanocapsules vaccine formulations, accessory signal stimulation, blocking the induction of Treg responses, and modulation of B cell maturation signals in the germinal centers (GCs) to improve memory B-cell and long-lived plasma cell generation. The specific aims are 1) To develop and formulate TLR5 ligand conjugates with cocaine for immunizations, to formulate these conjugates into nanocapsules with other TLR-based small molecule compounds, and to compare responses with standard carrier conjugate vaccines and alum adjuvant, 2) To improve COC-specific antibody responses by modulating B cell activation and germinal center responses, and 3) To enhance the immunogenicity and therapeutic potency of cocaine-TLR5 ligand conjugates and nanocapsules by manipulating Treg cell function.